1. Field of the Invention
The present invention relates to a method of removing mercury from waste incinerator exhaust gases and more particularly to a mercury removing method in which exhaust gases containing as constituents mercury and hydrochloric acid are washed with a washing liquid and the mercury is dissolved in the form of mercuric chloride and mercury forming complex ions with chlorine into the washing liquid thereby removing the mercury from the exhaust gases with high efficiency.
2. Description of the Prior Art
The harmful substances contained in the exhaust gases from a waste incinerator have heretofore been governed by the regulations from the standpoint of environmental pollution prevention. The harmful substances have included hydrogen chloride (HCl) and sulfur dioxide (SO.sub.2) and thus these harmful substances have been removed by harmful gas cleaning apparatus employing the dry process, the semi-dry process and the wet process.
Then, it has recently been found that the exhaust gases from waste incinerators have contained mercury in an amount exceeding the environmental guideline of 0.015 mg/m.sup.3 provided by the World Health Organization (WHO) and this has become an object of public concern.
In fact, however, the existing waste incinerator harmful gas cleaning apparatus of the dry, semi-dry and wet processes have all been designed to mainly remove hydrogen chloride (HCl) and sulfur dioxide (SO.sub.2) thus making the removal of mercury difficult and only the apparatus of the wet process have been capable of removing a trace amount of mercury.
On the other hand, the known means of removing the mercury from gases include the techniques of removing mercury from the hydrogen gas produced during the production of caustic soda by the mercury method. However, these techniques have been designed to remove the mercury entering as mercury vapor into the hydrogen gas from the electrolytic cell or the mercury accompanying the hydrogen gas produced. In other words, these techniques have been designed to remove the mercury present in the form of metal mercury in the hydrogen gas. On the contrary, the waste incinerator involves various chlorine generating factors, such as, chlorine gas and hydrogen chloride gas and these gases react with mercury. Thus, the mercury is mostly contained in the form of mercuric chloride in the exhaust gases. As a result, the known techniques of removing mercury from hydrogen gas, which have been used with the caustic soda production processes by the mercury method, cannot be applied as such to the removal of mercury, particularly mercuric chloride contained in the exhaust gas from a waste incinerator.